This invention relates to pre-treatment and electro-priming systems for paint lines, and more particularly, to an expandable horizontal travel/vertical dip pretreatment and electrodeposition system.
In modem paint systems used to paint automotive bodies (or other metal parts) that are exposed to the elements or other corrosive environments, the automotive body is first treated by the application of protective coatings before the color coat is applied. The process involves passing the body through several spay or immersion chemical baths, followed by immersion into an electro-deposition bath where a coating is applied.
One commonly used treatment system involves the application of a zinc phosphate or similar corrosion protection coating system followed by the application of a primer. The body is immersed in a zinc phosphate bath and, after removal from the zinc phosphate bath, is rinsed with chemicals and water to prepare the body for the electro-priming operation. The body is then immersed in an electro-coating tank, such as a cathodic or anodic electro-deposition paint primer tank, where a paint primer coating is deposited on the surface of the body through an electrolysis process. Subsequent rinses remove any undeposited primer. The body is then cured to get a protective primer coating. Once the body is finished with this treatment, a second coat of surface primer is optionally applied followed by a color topcoat and/or clear coat utilizing a separate paint line.
One type of pretreatment and electro-deposition system conventionally used for lower volume production in the auto industry is the vertical dip/horizontal travel type of system that utilizes a combination of immersion and spray stations. The bodies to be treated are horizontally indexed to a sequential series of stations. Some stations are vertical dip stations in which the body is lowered into a tank containing a treatment bath, such as zinc phosphate or a paint primer. Other stations are spray stations where the body is sprayed with a treatment spray or a rinse. The bodies remain at the stations for a set period of time. The stations are typically sized to handle one body at a time and the cycle time for the system is determined by the process that requires the longest amount of time to complete. This is typically the electro-deposition process or processes that are carried out in a vertical dip tank or tanks and require the body be immersed and, in the case of the electro-deposition process, under charge for around two to three minutes.
Treatment systems for higher volume production above about twelve jobs an hour typically utilize an overhead drag through conveyor systems or additional vertical dip systems. In a system of the overhead drag through conveyor system type, rather than indexing the body between stations, the body is continuously moved through the stations and in the case of a station having an immersion tank, such as an electro-deposition station, the body is immersed in the tank and dragged through the tank. The tank is sized so that the time that it takes to drag the body through is sufficient for the particular process to be completed. For example, as discussed above, electro-deposition requires that the body be immersed in the coating tank and under charge for approximately three minutes. Therefore, the electro-deposition tanks are sized so that it will take approximately three minutes to drag the body through them after full immersion.
The horizontal drag through systems are significantly more expensive than the vertical dip systems so that the vertical dip system is typically the system used for lower volume production of around ten to twelve jobs an hour or less. Given the limiting factor that each electro-deposition step requires a cycle time of about five minutes to transfer, immerse and process, vertical dip systems are typically capacity constrained to about ten to twelve jobs per hour. Additional vertical dip systems are typically used to achieve production volumes of above ten to twelve jobs per hour.
It is an object of this invention to provide a vertical dip pretreatment and electro-deposition system wherein the throughput limiting immersion tanks can have two sections with a bulkhead therebetween that divide them into two compartments or have removable end walls. With tanks having bulkheads dividing them into two sections, the bulkhead is removed to expand the tanks so that the product can be indexed through the tank thus permitting more than one product to be immersed in the tank at a time. With tanks having removable end walls, the removable end walls are removed and replaced with tank sections thus extending the tank size so that the extended tank functions similarly to the two section tank with its bulkhead removed.
A vertical dip pretreatment and electro-deposition system in accordance with this invention has immersion or dip tanks that are expandable. When production rates are below or up to the design capacity of the system, the expandable tanks are used unexpanded. If the expandable tank is the two-section bulkheaded divided type, only one compartment of each electro-deposition tank is used for the electro-deposition process and the product being treated will be immersed in that compartment. The other compartment is left dry and can be used as a storage or dump tank, thus eliminating the need for a separate dump tank. In operation, the product being coated is lowered into the specific tank for the specific treatment for the requisite process time and then raised out and moved to the next station in the system. When volume increases to above the design capacity of the system, the tanks are expanded either by removing the bulkheads, in the case of the two section bulkhead divided tanks, or by removing the removable end walls and replacing them with tank sections. Separate storage or dump tanks are then provided where required. In operation, the expanded system is set up so that when a product reaches an immersion station, it is lowered into the first section of the tank where the process begins. The product is then indexed or moved in the lowered position into the second section of the tank while the process continues. Upon completion of the process, the product is raised out of the tank and indexed to the next process station. Once the product moves out of the first section of an immersion tank, a second product can be lowered into the first section of the immersion tank to start that station's process on the second product. This effectively increases the production throughput of the system. Alternatively, each tank requiring expansion is expanded or lengthened sufficiently to permit the product to be dragged through it for the time needed for the process to complete.